The crustacean cardioactive peptide (CCAP) is a potent cardioexcitatory substance, originally identified in the pericardial organs of the shore crab, Carcinus means. It also modulates the neuronal activity in other arthropods. A CCAP-related new peptide family, the molluscan CCAP (M-CCAP) has been isolated and characterized from the snail Helix pomatia (Muneoka et al. 1994). Structural differences between the crustacean CCAP and the molluscan peptides are restricted only to the amidatedend of the molecules.